chore: improve log message in notification set

Improved log message for FFA_NOTIFICATION_SET, in
case caller doesn't have permissions to set notification.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Icdeced15190db874fe7f9e76c979dd34362f6135
diff --git a/src/api.c b/src/api.c
index e75105e..2ac9f91 100644
--- a/src/api.c
+++ b/src/api.c
@@ -3831,7 +3831,10 @@
 	if (!vm_notifications_validate_bound_sender(
 		    receiver_locked, ffa_is_vm_id(sender_vm_id), id_to_validate,
 		    notifications)) {
-		dlog_verbose("Notifications are bound to other sender.\n");
+		dlog_verbose(
+			"Sender %x not permitted to set notifications %x to "
+			"%x.\n",
+			sender_vm_id, notifications, receiver_vm_id);
 		ret = ffa_error(FFA_DENIED);
 		goto out;
 	}